Color flat panel displays, such as liquid crystal displays and the like, typically incorporate color filters used to provide pixels with color. One technique for fabricating color filters involves a laser-induced thermal transfer process. A particular prior art thermal transfer process is illustrated schematically in FIG. 1. A substrate 10, known in the art as a receiver element, is overlaid with a donor element 12, known in the art as a donor sheet. In the case of color filter fabrication, substrate 10 typically is made of glass and has a generally planar shape. Donor element 12 typically is a sheet that is relatively thin and relatively flexible when compared to substrate 10. Donor element 12 may be made of plastic, for example, and incorporates a transferable donor material (not shown) that may comprise a colorant, a pigment, or the like used to fabricate the color filter.
Donor element 12 is exposed to cause donor material to be transferred from selected portions of donor element 12 to substrate 10. Some exposure methods employ one or more controllable lasers 14 to provide one or more corresponding laser beams 16 to induce the transfer of donor material from the imaged regions of donor element 12 to corresponding regions of substrate 10. Controllable laser(s) 14 may comprise diode laser(s) which are relatively easy to modulate, are relatively low cost, and are relatively small in size. Such laser(s) 14 are controllable to directly expose donor element 12.
Once the selected regions of donor material have been transferred from donor element 12 to substrate 10, it is necessary to remove the used (“spent”) donor element 12 from substrate 10. For example, during typical fabrication of color filters, a first donor element 12 is used to apply one color, such as a red donor material to substrate 10, and the first donor element is then removed; a second donor element 12 is used to apply, for example, green donor material, and the second donor element is then removed; a third donor element 12 is used to apply, for example, blue donor material, and the third donor element is then removed.
In some instances, at the conclusion of each imaging process, the transferred donor material partially adheres to substrate 10 but also remains partially adhered to donor element 12. Such partial adherence of the donor material to both substrate 10 and donor element 12 can interfere in removing donor element 12 from substrate 10.
In a prior art technique, donor element 12 is removed from substrate 10 using a roller 18 incorporating one or more suction features 20. Roller 18 is brought into proximity of edge 12A of donor element 12 (as shown by arrow 19) and then suction is applied through Suction features 20, such that edge 12A of donor element 12 is secured to suction features 20. Roller 18 is then rotated (as shown by arrow 22) and translated (as shown by arrow 24) thereby to peel spent donor element 12 from substrate 10 and to wind spent donor element 12 onto the circumferential surface 18A of roller 18.
It has been found that the quality of color filters produced by the above process is a function of the contact pressure between peel roller 18 and donor element 12. In some instances, prior art peel roller 18, having a rigid core, is unable to provide sufficiently uniform pressure across its contact line with donor element 12 because of small irregularities on the chuck and support tables of the imaging engine.
What is needed in the art is a highly compliant peel roller that can apply gentle but substantially uniform pressure at all points of contact with the donor element despite such irregularities in the substrate.
It is a primary object of the invention to apply uniform pressure to a surface being traversed by a roller despite irregularities in such a surface.